1. Field of the Invention
The present invention relates to a vehicular headlamp of the projection type in which light emitted from a light source is reflected by an elliptic reflecting mirror, and a projecting lens collimates and projects forward the reflecting light. More particularly, the present invention relates to a vehicular headlamp of the projection type in which a discharge lamp is used for a light source.
2. Conventional Art
Recently, a discharge lamp has gradually been used for a vehicular headlamp because of its good light emission efficiency and attractive coloring. The discharge lamp disadvantageously generates ultraviolet rays when it emits light, which are harmful to the human body. The synthetic resin parts within the headlamp will degenerate with the ultraviolet rays. To eliminate such a problem, the discharge lamp is covered with a glove to intercept the harmful ultraviolet rays.
Where the discharge lamp with a glove is employed, a conventional headlamp of the type as shown in FIG. 1 does not involve problems as discussed below since, in the headlamp of this type, the rays of light emitted from a light source (discharge lamp bulb 1) are collimated by a parabolic reflector 2, and distributed by steps 5 formed on a lens 4.
However, the conventional headlamp of projection type with a glove as disclosed in coassigned U.S. patent application Ser. No. 681,017 and as shown in FIG. 2 suffers from the problems to be solved. In the headlamp of the projection type, the rays of light emitted from a light source (discharge lamp 1) is focused at a second focal position f of an elliptic reflector 3, and then are collimated and projected through a projection lens 6. As shown in FIG. 3, a hot zone 8 is undesirably divided into two parts. A luminous intensity is insufficient at the central portion 9 as shown in FIG. 3 or the mid portion between the divided hot zones.
The present inventors have found that the above problem arises from the fact that a part .lambda. shown in FIG. 2 of the reflected light from the reflector 3 is intercepted at the fore end of the ultraviolet-rays shield glove 1a. On the basis of this fact, we reached the conclusion that the problem could be solved by shaping the glove 1a to minimize the interception of the reflected light from the reflector 3.
On the other hand, FIG. 4 is a longitudinal sectional view showing the projection type conventional vehicular headlamp housed within a lamp body 62. A projection unit 61 is disposed within the lamp body 62. A lens holder 65, which holds a reflector 63 with a reflecting surface 63a, a discharge lamp 64, and a projection lens 65a are assembled into a single unit as the projection unit 61. A ultraviolet-rays shield glove 66, which covers the discharge lamp 64, is mounted to a base 4a of the discharge lamp 64.
In the structure, the glove 66 is hermetically closed. Accordingly, temperature within the glove 66 rises, possibly reducing the lifetime of the discharge lamp 64. The light reflected from the reflecting surface 63a is intercepted at the fore or top end of the glove 66, adversely influencing the distribution of light (the hot zone becomes dark).